Fully implement Kavenegar SMS support

Core changes:
- ISmsService: add SendBulkAsync (batches of 200) + GetAccountInfoAsync
- KavenegarSmsService: POST requests, sender number config, bulk send
  via comma-separated receptors, account balance, full error code mapping
  (HTTP 400-432), enabled-flag check before any send
- SmsMarketingService: replaced per-recipient loop with SendBulkAsync
- SmsController: new GET /sms/balance endpoint returns Kavenegar credit
- SmsDtos: SmsBalanceDto
- IntegrationDtos + PlatformIntegrationService: SenderNumber field
- appsettings.json + docker-compose: Kavenegar__SenderNumber = 90005671

Dashboard:
- sms-screen: char counter, SMS parts indicator (Persian 70/67 chars,
  Latin 160/153), account balance card, sender line display, result banner

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/Meezi.API/Controllers/SmsController.cs

@@ -11,16 +11,32 @@ namespace Meezi.API.Controllers;
 public class SmsController : CafeApiControllerBase
 {
     private readonly ISmsMarketingService _smsMarketingService;
+    private readonly ISmsService _smsService;
     private readonly IValidator<SendSmsCampaignRequest> _campaignValidator;
 
     public SmsController(
         ISmsMarketingService smsMarketingService,
+        ISmsService smsService,
         IValidator<SendSmsCampaignRequest> campaignValidator)
     {
         _smsMarketingService = smsMarketingService;
+        _smsService = smsService;
         _campaignValidator = campaignValidator;
     }
 
+    [HttpGet("balance")]
+    public async Task<IActionResult> GetBalance(string cafeId, ITenantContext tenant, CancellationToken cancellationToken)
+    {
+        if (EnsureCafeAccess(cafeId, tenant) is { } denied) return denied;
+
+        var info = await _smsService.GetAccountInfoAsync(cancellationToken);
+        var dto = info is not null
+            ? new SmsBalanceDto(info.RemainCredit, info.AccountType, true)
+            : new SmsBalanceDto(0, "master", false);
+
+        return Ok(new ApiResponse<SmsBalanceDto>(true, dto));
+    }
+
     [HttpGet("usage")]
     public async Task<IActionResult> GetUsage(string cafeId, ITenantContext tenant, CancellationToken cancellationToken)
     {